Waveguide radiator with perpendicular scattering posts at aperture

ABSTRACT

A WAVEGUIDE RADIATOR IS PROVIDED HAVING PERPENDICULAR SCATTERING POSTS PLACED WITHIN A SHAPED APERTURE END OF THE WAVEGUIDE TO PRODUCE A CIRCULARLY POLARIZED MICROWAVE RADIATOR AS A RESULT OF SPHERICALLY SCATTERING OF THE WAVES BY THE POSTS.

Jan. 5, 1971 w. M. SPANOS WAVEGUIDE RADIATOR WITH PERPENDICULARSCATTERING POSTS AT APERTURE Filed Aug. '7, 1968 (PR/0R ART) INVENTOR vWILL/AM M. SPA/V05 MJM ATTORNEY U.S. Cl. 343-756 .8 Claims ABSTRACT OFTHE DISCLOSURE A waveguide radiator is provided having perpendicularscattering posts placed within "a shaped aperture end of the waveguideto produce a circularly polarized microwave radiator as a result ofspherically scattering of th waves by the posts.

' BACKGROUND OF THE INVENTION In general this invention relates towaveguide radiators and more particularly to microwave high power,hemispherical coverage, circularly polarized radiators.

At low frequencies, where coaxial cables are used to transmit highpower, hemispherical coverage, circularly polarized antennas have beendesigned using crossed dipoles in front of a conical reflector. Atmicrowave frequencies, waveguide radiators must be used to handle highaverage powers which can range from two to 50 kilowatts. The designdescribed here. consists of a waveguide radiator which has thecapability of handling these high powers.

The basic problem in designing a'hernispherical cover,- age waveguideradiator is that of obtaining a sufiiciently broad E-plane and H-planepattern. With rectangular guide radiating a single polarization; broadH-plane coverage has been obtained by removing the side walls of theguide and inserting a scattering post in the mouth of the aperture. Abroader E-plane pattern can be obtained by closing up the aperture theE-plane.

SUMMARY OF THE INVENTION An object of this invention is to providc amicrowave, high power, hemispherical coverage, circularly polarizedwaveguide radiator.

Another object of this invention is to provide a circular polarizationover a broad beamwidth.

Still another object of this invention is to provide cooling means foruse during high power operation of the radiator.

According to the broader aspects of this invention, I have provided awaveguide having shaped aperture in which is mounted perpendicularscatteringposts which cooperate with said shaped aperture to produce aspace radiation pattern having a broad E-plane and H-plane.

A feature of this invention is that the scattering pins are designed topermit a coolant to flow therethrough for cooling the structure duringhigh power applications.

to the prior art; and

FIG. 2 illustrates the waveguide radiator according to the invention.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT To obtain a broaderpattern than from an ordinary waveguide, FIG. 1 shows a metallicscattering post 1 1; Patent 0 inside ,theaperturefi, at its center. Thewaveguide corners 4 have been removed by a symmetrical cut so as to pro-;duce the broadened-pattern." In the arrangement, according to the priorart, the beam broadening occurs in the H-plane so that a broad beamlinearly polarized wave guide radiator results. A broader E-planepattern can be obtained by closing up the aperture in the E-plane.

Therefore, to obtain a broad pattern for two simulta- .neous orthogonalpolarizations which are required for circular polarization, a square orcircular waveguide must be used with symmetrically shaped side walls andsymmetrical scattering posts, FIG. 2 shows how the circularly,polarized. hemispherical coverage antenna is structured.

Asquare waveguide 5 is shown for purposes of illustratio'n into -whichis coupled acircularly polarized input 6. Symmetrical scattering posts 8having a diameter d and a'length L are mounted within the shapedaperture end 7 of the waveguide to provide a symmetrical radiator. Thesymmetrically shaped aperture 7 has an effective diameter D and a lengthl which has been removed from all four corner sections of the waveguide5. In the case of the circular waveguide, the removed portions would be90 apart and at the effective diameter D. The scattering posts 8 arehollow and connected to coolant line inputs 9 and cooling line odtputs10.

Control of the radiation pattern in the H-plane is accomplished byselection ofthe diameter of d and the length l of the waveguide wallwhich is removed. Control of the radiation pattern in the E-plane isaccomplished by control of the effective diameter D of the waveguide andthe length L of the scattering post 8 which is also the separation ofthe parallel walls.

Dielectric loading is used in the aperture region 7 so that the initialdiameter of the aperture is as small as possible and the pattern of thesquare waveguide is as broad as possible without the additional patternbroadening means. Teflon can be used for the dielectric loading becauseits loss is low and it can withstand the resultant temperature riseswhich occur. For broadband impedance matching a quartz" dielectricmatching section can be inserted within the dielectrically loadedwaveguide.

Cooling must be provided for the aperture region of the radiator. Thedielectric, and copper losses will be greatest in the mouth ofjtheaperture because of the fringing fields which occur and because of themanner by which the radiation is being forced. In addition, thescattering posts are driven strongly in order to produce a radiationback toward the input throat of the waveguide. This will causeconsiderable heat to be generated in the posts which must be removed toprevent an unreasonable temperature rise.

The means for preventing the temperature rise is to provide cooling byforcing liquid coolant through the interior of the posts. The liquid canbe removed through the coolant output lines so as to provide continualcirculation through the posts. The coolant lines 9, 10 are made ofcopper and run along the metallic forces of the transition and thewaveguide to conduct heat away from the aperture region.

Tests results indicate that the following characteristics are typical ofa radiator according to the design described herein:

Frequency: 4400-5000 mc.

SWR: Less than 1.25

Power: 10-20 kw. average Polarization: Circular Pattern Coverage: idegrees from the axis of radia- .tor (200 degree spherical sectoromnidirectional around axis).

According to illustrated embodiment I have shown and described awaveguide radiator having an aperture produced by cutting away thecorners of the waveguide and placing within the mouth of said aperturescattering posts to provide a circularly polarized high poweredmicrowave antenna which results from spherically scattering the inputwave by the symmetrical scattering posts. Also, the scattering posts aredesigned hollow so that a coolant may flow therethrough for cooling thestructure during high powered power applications.

While I have described above the principles of my invention according tospecific apparatus, this description is to be considered only by way ofexample and not as a limitation to the scope of my invention as setforth in the objects and features thereof and in the accompanyingclaims. I i.

I claim:

1. A hemispherical coverage waveguide radiator comprising:

a symmetrical waveguide;

perpendicular scattering posts mounted within a shaped aperture of saidwaveguide which cooperates with said posts to determine the spaceradiation pattern; and

a circularly polarized input wave coupled to said waveguide, whereby, abroad E-plane and H-plane pattern is radiated due to the sphericalscattering of said input wave by said posts.

2 A radiator according to claim 1 wherein said perpendicular scatteringposts are symmetrical shaped and mounted to symmetrical portions of saidshaped aperture.

3. A radiator according to claim 2 wherein:

said H-plane radiation pattern is controlled by the diameter (d) of thescattering posts and the length (l) of the waveguide wall which has beenremoved; and

said E-plane radiation pattern is controlled by the diameter (D) at themouth of said aperture and the length (L) of the scattering posts. v

4. A radiator according to claim 3 wherein said posts are hollow and.have a coolant flowing therethrough for cooling the structure duringhigh power applications.

5. A hemispherical coverage waveguide radiator for radiating acircularly polarized microwave comprising:

a square Waveguide having its corner portions removed; perpendicularscattering posts symmetrically mounted in the aperture mouth of saidwaveguide, the combined configuration determining the space radiationpattern; and t i a circularly polarized input wave coupled to saidwaveguide, whereby, a broad E-plane and H-plane pattern is produced bythe spherical scattering of said input wave by said posts.

6. A radiator according to claim 5 wherein said perpendicular scatteringposts are symmetrical shaped and mounted to the remaining symmetricalportions of the side walls of said waveguide.

7. A radiator according to claim 6 wherein:

said H-plane' radiation pattern is controlled by the diameter (d) of thescattering posts and the length (l) of the waveguide corners which hasbeen removed from the walls; and

said E-plane radiation pattern is controlled by the diameter (D) at themouth of said aperture and the length (L) of the scattering postsbetween the walls 8. A radiator according to claim 7 wherein said postsare hollow and have a forced liquid coolant flowing through the interiorof the posts during high power applications.

References Cited UNITED STATES PATENTS 2,756,419 7/1956 Foley et al.343-772 3,382,501 5/1968 Fee 343-772 3,445,852 5/ 1969 Karlson 343-772FOREIGN PATENTS v 787,756 12/1957 Great Britain 343786 ELI LIEBERMAN,Primary Examiner US. Cl. X.R. 343--786

